Alpha, beta, gamma, and delta tocopherol and alpha, beta, gamma, and delta tocotrienol (hereafter such tocopherols and tocotrienols are referred to collectively as tocols) can be found in various ratios and concentrations in crude vegetable oils such as soybean, sunflower, canola, rapeseed, cottonseed, palm oil, and rice bran oil. Tocols are valuable constituents of vegetable oil and have a number of practical applications. For example, tocols help prevent the oxidation and spoilage of food. Tocols are also valuable dietary supplements because they can reduce the risk of certain types of cancer.
During the refining of vegetable oils, a large fraction of tocols are lost to various by-product and waste streams. These by-product and waste streams include, but are not limited to, deodorizer distillates, steam refining distillates, and acidulated soapstocks. The vegetable oil refining by-products typically contain from less than 1% to greater than 20% tocols by weight. Thus, the oil refining by-products are a valuable source of tocols.
The by-product streams that contain the tocols also contain from 20 to 99% by weight free fatty acids, less than 1% to 20% by weight sterols, less than 1% to 20% by weight sterol esters of fatty acid, less than 1% to 40% by weight mono, di, and triglycerides, less than 1% to 30% by weight hydrocarbons, and other compounds present in significant amounts. Thus, in order to obtain a useful tocol concentrate stream, it is necessary to remove these substances.
Numerous methods have been proposed for the recovery of tocols from vegetable oil refining by-products. Tocols can be removed from tocol-containing mixtures by subjecting the mixture to a series of distillations. U.S. Pat. Nos. 5,512,691; 5,660,691; and 5,487,817 disclose that a tocol concentrate can be obtained from a deodorizer distillate by esterification of the sterols with the free fatty acids already present in the mixture, and subjecting the esterified product to a series of distillation steps to provide a tocol concentrate stream. EP 610742 A and JP 60185776 A also disclose the separation of tocopherols from fat residues using distillation techniques. None of these references, however, disclose an extraction step for separating a tocol from a tocol-containing mixture.
JP60048981A and JP60149582A discloses that tocopherols can be concentrated by extraction of a tocopherol containing substance with supercritical carbon dioxide, which is a non-polar, organic solvent that is immiscible with water under supercritical conditions. Moreover, these methods require the use of expensive, high-pressure equipment capable of withstanding pressures of at least 73 bar.
DE 3615029 discloses the purification of tocopherols by contacting a tocopherol containing substance with neat methanol to form two layers, separating the methanol layer, cooling the methanol layer to produce a methanol phase and a raffinate layer, and recovering the tocopherols from the methanol layer. A disadvantage of this method is that a considerable amount of tocopherols are lost to the raffinate, thereby reducing the overall recoverable yield. U.S. Pat. No. 4,550,183 discloses extracting a tocopherol containing material with caustic methanol to produce a two phase system. The methanol layer is removed and neutralized with acid. A disadvantage of this method is that an additional step is required to neutralize the basic methanol layer. JP 03127730 A discloses extracting an unsaturated oil or fat with a neat extraction solvent composed of neat butanol, ethylene glycol, methyl ethyl ketone, acetone, benzene, or cyclohexane followed by a series of distillation steps.
Another approach for increasing the concentration of tocols is to add an esterifying agent such as an alcohol to convert the free fatty acids present in the tocol-containing mixture to the corresponding ester followed by distillation to remove the tocol. For example, U.S. Pat. No. 2,432,181 discloses that tocopherols can be recovered from vegetable oils and fats by reacting the fatty acid glycerides with an aliphatic monohydric alcohol in the presence of an alkaline alcoholysis catalyst, followed by a flash distillation. U.S. Pat. No. 3,153,055 discloses a process for the isolation of sterols and tocopherols from deodorizer distillate by esterification of free fatty acids and glycerides using lower monohydric alcohol esters under strongly acidic conditions. U.S. Pat. No. 3,335,154 discloses that deodorizer distillate is saponified and acidulated to convert glycerides and sterol esters to free fatty acids and free alcohols (glycerol, sterols respectively). The free fatty acids are esterified with a monohydric lower alcohol and mineral acid catalyst. The sterols are precipitated/crystallized by the addition of water to the mixture, and the tocopherols are concentrated by removal of the fatty acid esters by molecular distillation. U.S. Pat. No. 4,454,329 describes that a tocopherol concentrate can be obtained from deodorizer distillates by esterification of the free fatty acids with a dihydric or polyhydric alcohol, in the presence or absence of an acid catalyst.
The addition of alcohols has a number of drawbacks. The addition of extraneous monohydric alcohols results in the production of fatty acid esters, which are not normally present in the vegetable oil by-product feed material. The excess monohydric alcohol must be removed in an additional processing step. Additionally, to produce a highly concentrated tocopherol product, the sterols must either be removed by crystallization or by other means. Finally, saponification of the fatty acids requires large amounts of caustic acid for acidulation, which creates excessive salt wastes.
In light of the above, one object of this invention is to provide an efficient method for separating tocols from a tocol-containing mixture.
Another object of the present invention is to provide a method for separating tocotrienols from a tocol-containing mixture. Tocotrienols have been shown to treat or prevent a number of human diseases. Preliminary medical research has shown that tocotrienols, particularly gamma-tocotrienol, can reduce the proliferation of breast cancer especially when used in conjunction with other anti-cancer drugs (Nesaretnam K, Guthrie N, Chambers A F, and Carrol K K Lipids 1995 30 1139; and Guthrie N, Gapor A, Chambers A F, and Carroll K K J. Nutr. 1997 127 544S). Tocotrienols are also of special interest for their hypocholesterolemic effects, as they decrease the blood level of the low density lipoprotein fraction of cholesterol and the total serum cholesterol, while increasing the ratio of the high density lipoprotein fraction of cholesterol to the low density lipoprotein fraction. Such effects have been shown to be clinically significant in lowering the risk of heart disease. (T. Gordon, et al., "High Density Lipoproteins as a Protective Factor Against Coronary Heart Disease", The American Journal of Medicine, 62, pp. 707-714 (1977)).
Thus, it would be desirable to have a method for isolating increased quantities of tocotrienols.
Another object of the present invention is to provide a method for separating tocopherols from a tocol-containing mixture. In particular, alpha-tocopherol can reduce the risk of stomach and prostrate cancer. Thus, there is presently a high demand for increased quantities of tocopherols.
The prior art methods for increasing the tocol concentration are inefficient with respect to the number of steps required to separate the tocols as well as the overall yield of the recovered tocols. Additionally, there are no explicit methods in the prior art for the production of increased quantities of tocotrienols. The present invention discloses efficient methods for separating tocols and/or tocotrienols from a tocol-containing mixture.